Heat Treating Apparatus

ABSTRACT

[Problems] To prevent both slips caused by damage from projections, and slips caused by adhesive force occurring due to excessive smoothing. 
     [Means for Solving the Problems] The heat treating apparatus includes a processing chamber for heat treating wafers and a boat for supporting the wafers in the processing chamber. The boat further includes a wafer holder in contact with the wafer and a main body for supporting the wafer holder. The wafer holder diameter is 63 to 73 percent of the wafer diameter, and the surface roughness Ra of the portion of the wafer holder in contact with the wafer is set from 1 μm to 1,000 μm. The wafer can be supported so that the amount of wafer displacement is minimal and both slips due to damage from projections on the wafer holder surface, and slips due to the adhesive force occurring because of excessive smoothing can be prevented in that state.

TECHNICAL FIELD

The present invention relates to a heat treating apparatus and relatesin particular to technology for supporting the substrate for processing,and for example, relates to technology effective in the heat treatmentprocess performed at a comparatively high temperatures to thermallytreat the semiconductor wafer (hereafter called, wafer) where the IC isformed in a method for manufacturing semiconductor integrated circuitdevices (hereafter called IC).

BACKGROUND ART

A batch type vertical hot-wall heat treating apparatus is widely used inheat treatment processes such as oxidizing, diffusion or annealingprocess applied to the wafer at comparatively high temperatures in ICmanufacturing methods.

This batch type vertical hot-wall heat treating apparatus (hereaftercalled, heat treating apparatus) includes a process tube installedvertically to form the processing chamber where the wafers are carriedin; a heater unit for heating the processing chamber outside the processtube; a boat loaded into and out of the processing chamber, supportingmultiple wafers on multiple stage support grooves; and a standby chamberfor keeping the boat to be loaded into or out of the processing chamberin a stand-by state.

After the multiple wafers are charged (wafer charging) in the boat inthe standby chamber, they are loaded (boat loading) from the standbychamber into the preheated processing chamber. The wafers are thensubjected to the desired heat treatment because the processing chamberis heated to the specified heat treating temperature by the heater unit.

The boat in conventional heat treating apparatus of this type, includesa pair of upper and lower edge plates, three piece support membersinstalled for example vertically in between both edge plates, andmultiple support grooves formed at equidistant intervals longitudinallyon the three piece support members and formed with openings mutuallyfacing each other. The multiple wafers are supported horizontally whilearrayed with their centers mutually aligned because they are inserted inthe support grooves of the three piece support members.

However, boats with this type of structure possess the followingproblems. The entire weight of the wafer is supported only by the threesupport grooves so that when a thermal stress is suddenly applied to thewafer, a crystallizing flaw (slip) then occurs due to its own weightstress and the tensile stress on the contact surface between the waferand support grooves, and warping occurs on the wafer.

The wafer holder in patent document 1 was disclosed as technology forresolving the problem.

This wafer holder was formed from silicon carbide (SiC) in a circularring shape for supporting the periphery of the wafer. This wafer holderdispersed and supported the total weight of the wafer along the entirecircumference and in this way reduced the gravitational force applied tosupport points on the wafer contacting the wafer holder and alsoprevented wafer slip and damage as well as wafer warping.

Patent document 1: Japanese Patent Non-examined Publication No. 7-45691

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

Damage is generally formed on the rear surface of the wafer from thewafer's own weight due to contact between the wafer and protrusions onthe support portion. It is considered that the strain caused by thisdamage is what makes slipping occur. The “slip suppression” means of theconventional art was to reduce the frictional force acting on the waferand support portion by forming a smooth surface on the support portionthat supports the wafer in order to eliminate protrusions.

However, slips not caused by damage from protrusions were confirmed tooccur when the surface on the support portion was smoothed too much.Here, excessive smoothing of the support portion surface induces anadhesive force at the boundary between the wafer and support portion (abonding force caused by intermolecular force of the molecules on thesurface between the two materials) so that slipping occurs when thewafer and support portion stuck to each other are separated (See FIG.15A and FIG. 15B)

An object of the present invention is to prevent slips caused by anadhesive force from excessive smoothing, as well as prevent slips causedby damage from protrusions.

Means for Solving the Problem

The typical present invention is described next.

(1) A heat treating apparatus comprising: a processing chamber for heattreating a substrate, and a support tool for supporting the substrate inthe processing chamber; and the support tool includes a support platewhich contacts the substrate, and a main body for supporting the supportplate; and characterized in that the diameter of the support plate is 63to 73 percent of the diameter of the substrate and also in that thesurface roughness Ra of at least a portion of the support plate whichcontacts the substrate is set from 1 μm to 1,000 μm.

(2) A heat treating apparatus according to the above item (1),characterized in that the surface roughness Ra of at least the portionof the support plate which contacts the substrate is set from 1.5 μm to1,000 μm.

(3) A heat treating apparatus according to the above item (1),characterized in that the surface roughness Ra of at least the portionof the support plate which contacts the substrate is set from 2 μm to1,000 μm.

(4) A heat treating apparatus according to the above item (1),characterized in that the diameter of the substrate is 300 mm, and thediameter of the support plate is 190 mm to 220 mm.

(5) A heat treating apparatus according to the above item (1),characterized in that the hardness of at least the portion of thesupport plate which contacts the substrate is the same as or greaterthan the hardness of the substrate.

(6) A heat treating apparatus according to the above item (1),characterized in that the main body is made from silicon carbide, andthe support plate is made from silicon or silicon carbide.

(7) A heat treating apparatus according to the above item (6),characterized in that a layer of silicon oxide, silicon carbide, orsilicon nitride is formed on the surface of the support plate.

(8) A heat treating apparatus according to the above item (1),characterized in that the heat treatment is performed at a temperatureof 1300° C. or higher.

(9) A heat treating apparatus according to the above item (1),characterized in that at least one through hole is formed in the supportplate.

(10) A method for manufacturing a substrate comprising the steps of:

supporting a substrate on a support plate in which the diameter is 63 to73 percent of the substrate diameter, and the surface roughness Ra of atleast the portion which contacts the substrate is 1 μm to 1,000 μm;

loading the substrate supported on the support plate into a processingchamber;

heat treating the substrate supported on the support plate in theprocessing chamber; and

unloading the substrate from the processing chamber after the heattreating.

EFFECT OF THE INVENTION

The invention according to the above item (1) is capable of supportingthe substrate so that the amount of the substrate displacement(deflection) is minimal. Moreover, when supporting the substrate in thatstate, the invention is capable of preventing both slips due to fromprotrusions on the surface of the support plate, and slips due to theadhesive force occurring due to excessive smoothing of the support platesurface.

The invention according to the above item (2) is capable of reliablypreventing both slips when supporting the substrate so that the amountof the substrate deflection is minimal.

The invention according to the above item (3) is capable of preventingboth slips to an even greater degree of reliability when supporting thesubstrate so that the amount of the substrate displacement is minimal.

The invention according to the item above (4) can render the sameeffects as in the above item (1).

The invention according to the above item (5) can render the sameeffects as in the above item (1) even when the hardness of at least theportion of the support plate which contacts the substrate is the samehardness or larger than the substrate hardness.

The invention according to the above item (6) can render the sameeffects as in the above item (1) even when the main body is made fromsilicon carbide, and the support plate is made from silicon or siliconcarbide.

The invention according to the above item (7) can render the sameeffects as in the above item (1) even when a layer made from siliconoxide, silicon carbide, or silicon nitride is formed on the surface ofthe support plate.

The invention according to the above item (8) can render the sameeffects as in the above item (1) even when the heat treating isperformed at temperatures of 1300° C. or more.

The invention according to the above item (9) can render the sameeffects as in the above item (1) even when at least one through hole isformed in the support plate.

The invention according to the above item (10) can render the sameeffects as in the above item (1).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a partly abbreviated front cross sectional view showing theoxidizing device of an embodiment of the present invention;

FIG. 2 is a front cross sectional view showing the main essentialsection;

FIG. 3 is a perspective view showing a portion of the support groove ofthe boat;

FIG. 4 is a diagram view showing a contact model between the flatsurface and semi-spherical protrusion;

FIG. 5A and FIG. 5B are drawings showing a support model of a piece ofcontinuous semi-spherical protrusions. FIG. 5A is an enlargedfragmentary view. FIG. 5B is a view of the overall section.

FIG. 6 is a graph showing the interrelation between the perpendicularload and adhesive force and the friction coefficient.

FIG. 7 is a graph showing the interrelation between the radius ofcurvature Rp and perpendicular load acting on each unit of surface areaper the support points and the friction coefficient μ.

FIG. 8A and FIG. 8B are drawings showing the oxidizing device of anotherembodiment of the present invention. FIG. 8A is a plane cross sectionalview showing the support groove section of the boat. FIG. 8B is a partlyabbreviated front view.

FIG. 9 is a graph showing analysis results for the interrelation of thedeflection amount at the center, the wafer edge and support position onthe wafer holder support model and the 4-point support model.

FIG. 10A and FIG. 10B are diagram views showing the model used in theanalysis. FIG. 10A is a drawing showing the wafer holder support model.FIG. 10B is a drawing showing the 4-point support model.

FIG. 11A and FIG. 11B are photographs showing results of the heattreating with the 4-point model at a position of radius of 100 mm. FIG.11A is an observation photograph of the entire surface of the wafer madeby a surface inspection device. FIG. 11B is an optical microscopephotograph of the wafer rear surface.

FIG. 12A and FIG. 12B are photographs showing results from heat treatingwith the wafer holder support model with a diameter of 180 mm. FIG. 12Ais an observation photograph of the entire surface of the wafer made bya surface inspection device. FIG. 12B is an optical microscopephotograph of the wafer rear surface.

FIG. 13 is a diagram showing a model for finding the surface roughnessRa.

FIG. 14 is a graph showing the interrelation between the surfaceroughness Ra and the surface maximum height Ry.

FIG. 15A and FIG. 15B are photographs showing processing results on thewafer whose surface roughness Ra is in the “slip-occurs” region. FIG.15A is an observation photograph made by a surface inspection device.FIG. 15B is a microscope observation photograph of slips from damage asa start point.

FIG. 16A and FIG. 16B are photographs showing processing results on thewafer whose surface roughness Ra is in “slip-free” region. FIG. 16A isan observation photograph made by X-ray topograph. FIG. 16B is amicroscope photograph of the small damages on the wafer edge.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention is described next while referringto the accompanying drawings.

In the present embodiment, the heat treating apparatus of the presentinvention is structurally comprised of a heat treating apparatus (batchtype vertical hot-wall heat treating apparatus) as shown in FIG. 1 andFIG. 2; and functionally is comprised of a dry oxidizing device(hereafter simply called an oxidizing device) as one type of oxidationfilm forming apparatus for forming an oxidization film on a wafer.

An oxidizing device 10 contains a process tube (reaction tube) 12. Theprocess tube 12 is made from quartz (SiO₂) or silicon carbide (SiC) andformed in an integrated cylindrical shape with the bottom end opened andthe top end closed. The process tube 12 is installed vertically so thatits centerline is perpendicular and is supported by an installationchamber 11 a at the upper portion of a case 11.

The hollow section within the process tube 12 forms a processing chamber13. The processing chamber 13 is structured to allow load-in of a boat21 supporting multiple concentrically arrayed wafers 1. The bottom endopening of the process tube 12 forms a furnace opening 14 for loadingthe boat 21 in and out.

Multiple flow holes 15 are formed in the thickness direction in thesealed wall (hereafter called ceiling wall) on the top end of theprocess tube 12 to allow the gas to disperse across the entireprocessing chamber 13. A gas pool 16 is formed on the ceiling wall ofthe process tube 12 to cover the flow holes 15.

A heat equalizer tube 17 is provided concentrically outside the processtube 12. This heat equalizer tube 17 is also supported by the case 11.The heat equalizer tube 17 is made from silicon carbide (SiC) and formedin an integrated cylindrical shape with the bottom end opened and thetop end closed.

A heater unit 18 is installed in a concentric circle so as to enclosethe heat equalizer tube 17 on the outer side of the heat equalizer tube17. The heater unit 18 is also supported by the case 11. A thermocouple19 is installed facing upward and downward between the process tube 12and the heat equalizer tube 17. This heater unit 18 is structured toheat the entire interior of the processing chamber 13 to a specifiedtemperature distribution or a unified temperature distribution bycontrol of the controller (not shown in the drawing) based on thetemperature detection of the thermocouple 19.

An exhaust pipe 32 at the bottom section on the side wall of the processtube 12 is connected with the processing chamber 13. The exhaust pipe 32connects to one end of an exhaust line 33. An exhaust apparatus 34comprised of a blower and vacuum pump, etc. is connected to the otherend of the exhaust line 33. A pressure regulator 35 is installed on theway of the exhaust line 33. This pressure regulator 35 controls thepressure of the processing chamber 13 to a specified pressure via acontroller (not shown in the drawing) based on detection results from apressure sensor 36 connected on the way of the exhaust line 33.

A supply pipe 37 is installed on the outer side of the process tube 12.This supply pipe 37 extends upward and downward along a section of theprocess tube 12 and the top end of this supply pipe 37 connects to thegas pool 16. A process gas supply line 38 connects to the bottom end ofthe supply pipe 37. An oxygen gas supply line 41 connected to an oxygen(O2) gas source 40; and a nitrogen gas supply line 43 connected to anitrogen gas (N2) source 42 are respectively connected to this processgas supply line 38.

A seal cap 20 formed in a disk shape roughly equivalent to the outerdiameter of the process tube 12 is installed concentrically directlybelow the process tube 12 in the standby chamber 11 b which is the lowerchamber of the case 11. The seal cap 20 is structured to be raised andlowered vertically by a boat elevator (not shown in the drawing)comprised by a feed screw mechanism. The boat 21 functioning as asupport tool to support the substrate is supported vertically on theseal cap 20.

The boat 21 is made from silicon carbide. The boat 21 is comprised of apair of end plates 22, 23 at top and bottom, and multiple supportmembers (three pieces in this example) 24 installed perpendicularlybetween both end plates 22, 23. Support grooves 25 in numerous steps areformed longitudinally at equal distances facing each other at the samestep in the support member 24.

An R chamfer section 27 is formed on the outer circumference edge of asupport surface 26 formed from the upward facing surface of each supportgroove 25 as shown in FIG. 3. The radius of curvature of the R chamfersection 27 is set to 1 mm or more.

The surface of the support surface 26 portion which contacts the wafer 1is set to a surface roughness (Ra) between 10⁻⁶ m (1 μm) and 10⁻³ m(1000 μm). The outer circumferential portion of the wafer 1 is insertedand supported on the support grooves 25, 25, 25 on the same stage of thethree support members 24, 24, 24. The support surface 26 supporting thethree points on the periphery of that lower surface is set to a surfaceroughness (Ra) from 10⁻⁶ m to 10⁻³ m. The multiple wafers 1 are arrayedhorizontally and mutually along the center of the boat 21 whilerespectively supported on these support grooves 25.

The methods for setting the surface configuration and roughness of thesupport portion which is the characteristic of the present invention forsupporting the wafer 1 while in contact with the lower surface of thewafer 1 are described next.

Damage from the wafer's own weight is usually formed on the wafer due tocontact of the wafer and protrusions on the support portion. It isconsidered that the strain caused by this damage causes slips to occur.Therefore, damage caused by the wafer's own weight must be limited inorder to prevent slips from occurring (hereafter called slip-free).Moreover, the force created by the protrusion must be reduced in orderto limit damage due to the wafer's own weight.

The friction force Ff acting on the support portion and wafer isgenerally expressed by multiplying the perpendicular load L from thewafer's own weight by the friction coefficient μ as shown in thefollowing formula (1) (Coulomb's law).

Ff=μ×L  (1)

One method often used to achieve a slip-free is to lower the frictioncoefficient μ between the wafer and the support portion by making thesurface of the portion which supports the wafer as smooth as possible.

However, the friction coefficient μ is basically a fixed value.Smoothing the surface of the support portion is actually to reduce thefrictional force acting on each support point by increasing the numberof tiny support points to divide the perpendicular load.

Contact between the wafer and the support portion is here assumed ascontact between a semi-spherical protrusion and a level surface (wafer)as shown in FIG. 4.

In FIG. 4, R is the radius of curvature of the semi-sphericalprotrusion, a is the radius of the damage formed on the surface by thesemi-spherical protrusion, h is the depth of that same damage, and A isthe surface area of that same damage. The surface area A of the damageis called the true contact surface area. When two materials make contactat a perpendicular load L, the soft material (material with small yieldstress) deforms plastically, and the surface area that deforms until thestress on the contact surface becomes equal to the yield stress (σ) isthe true contact surface area A. This true contact surface area A isexpressed by the following formula (2). The value for the true contactsurface area A is a characteristic value for two materials in contactwith each other and is not dependent on the state of the surface.

A[m² ]=L[N]/σ[Pa]  (2)

The following description here assumes the case where a piece withcontinuous multiple semicircular protrusions is supporting the wafer asshown in FIG. 5A and FIG. 5B.

The perpendicular load made up of “wafer's own weight L/number P ofsupport points” is applied to each of the multiple semi-sphericalprotrusions. In the symbols used from here onward, a “p” attached to acharacter signifies “per each support point”.

A large surface roughness (Ra) is a state as shown in FIG. 5A, where theradius of curvature (Rp) of the semi-spherical protrusions is large, andthere are few support points. A small surface roughness (Ra) is a stateas shown in FIG. 5B, where the radius of curvature (Rp) of thesemi-spherical protrusions is small, and there are many support points.

When the radius of curvature of the semi-spherical protrusions is large,then there is a large frictional force acting on each support point sothat damage formed on the wafer is deep and becomes large. Therefore,slips easily tend to occur from this damage as the start point.Conversely, when the radius of curvature of the semi-sphericalprotrusions is small, the perpendicular load acting on each supportpoint is reduced, which inhibits the forming of damage that becomes thestart point for slipping.

However, the friction coefficient μ is extremely large under conditionswhere the perpendicular load is extremely small as shown by the solidline curve in the graph in FIG. 6 that shows the interrelation betweenthe perpendicular load and the adhesive force and the frictioncoefficient. This result occurs because friction force Ff is actuallyexpressed as a size just as shown in the following formula (3), bymultiplying a fixed apparent friction coefficient (μ′) at the boundarysurface by the sum of the perpendicular load L and the “adhesive forceFa”. The source for FIG. 6 and the observations is as follows.

Yasuhisa Ando, “Micromachine and Tribology”, Surface Science, 1998, Vol.No. 19, Issue No. 6, p. 385-391

Here, the “adhesive force F” is the binding force from theintermolecular force (Van der Waals force) of the molecules on thesurface between two materials.

Ff=μ′(L+Fa)  (3)

Here, the adhesive force Fa is expressed by the following formula (4)from the JKR theory assuming use of the contact model shown in FIG. 4.

Fa=3/2×γπR  (4)

In formula (4), γ is the characteristic surface energy of the material.In the case of Si (100), the surface energy is 2.13[N/m]. One can seefrom formula (4) that the adhesive force Fa is proportional to theradius of curvature R of the semi-spherical protrusion.

The friction coefficient μ is derived via formula (1) and formula (3) asexpressed in the following formula (5).

μ=μ′(L+Fa)/L  (5)

However, Fa=p×Fap  (6)

FIG. 7 is a graph showing the relation between the radius of curvatureRp, and the perpendicular load acting per unit of surface area on eachsupport point and the friction coefficient μ. In FIG. 7, the truecontact surface area A is approximately calculated for a heat treatingprocess of “1350° C.” from the previously known silicon yield stressvalue and silicon yield stress value obtained in a heat treating processimplemented at “1200° C.” in a prior evaluation, and applied to formula(5). The apparent friction coefficient μ′ at this time is set as a fixedvalue “1”.

In areas where the radius of curvature of the semicircular protrusionsis small (smooth flat surface), the friction coefficient μ increasessharply due to the dominant adhesive force Fa, and one can see that alarge friction force Ff is acting between the wafer and support portion.Conversely, the load acting per unit of surface area on each supportpoint increases along with the radius of curvature (Rp).

The formation of damage due to protrusions must be suppressed (The loadacting on each protrusion must be reduced) and friction force Ff actingbetween the wafer and support portion must be reduced in order toprevent the occurrence of slips. To achieve these goals, in FIG. 7, asurface state with the radius of curvature Rp balanced in the followingtwo areas must be achieved.

1) Area with small friction coefficient μ

2) Area with small perpendicular load per each support point

In FIG. 7 for example, when the continuous protrusions have a radius ofcurvature of 10⁻⁶ m or more, then the friction coefficient (μ) may be aslarge as “10” and the perpendicular load is a small 10⁻⁴ [N/point/m²] sothat slips caused from damage by protrusions are not likely to occur.

In case of continuous protrusions smaller than this, the perpendicularload becomes even smaller but the friction coefficient (μ) that affectsthe adhesive force increases so that damage is formed due to theadhesive force in the portion where the protrusions and wafer makecontact and slips occur due to this factor.

Conversely, when the “large” continuous protrusions have a radius ofcurvature of 10⁻³ m or more, then the friction coefficient issufficiently small but the perpendicular load per each support pointbecomes large, and slips caused from damage by protrusions are prone tooccur.

In other words, an ideal wafer support surface is a surface withcontinuous protrusions whose radius of curvature is betweenapproximately 10⁻⁶ m and 10⁻³ m. The surface roughness (Ra) calculatedat this time is a figure between approximately 10⁻⁶ m and 10⁻³ m.

Deriving the surface roughness Ra utilized in the actual evaluation andthe friction coefficient μshown in FIG. 7, from the semi-sphericalprotrusions shown in FIG. 4 is described here.

Calculating each parameter for each support points is described first.The true contact surface area A is the surface area of the section cutout from the semicircular protrusion with the radius of curvature R bythe radius “a” (radius of damage). Setting the angle as θ at the heighth of the cut out section yields the following formula.

A=2πR ²(1−sin θ)  (7)

a=R cos θ  (8)

h=R(1−sin θ)  (9)

Here, by setting the damage depth h divided by the radius a of thedamage as the cut-in amount Dp, we derive the remaining elements asfollows.

Dp=h/a  (10)

a=[A/{π×(1+Dp ²)}]^(1/2)  (11)

h=a×Dp=Dp×[A/{π(1+Dp ²)}]^(1/2)  (12)

R={A×(1+Dp ²)/(4πDp ²)}^(1/2)  (13)

When supporting at support points of number P, the true contact surfacearea A and the perpendicular load are divided by the number P of supportpoints.

Ap=A/P  (14)

Lp=L/P  (15)

Applying this to the formulas (3), (4), (11) and (13) yields:

Ffp=μ′(Lp+Fap)  (16)

Fap=3/2×γπRp  (17)

ap=[Ap/{π×(1+Dp ²)}]^(1/2)  (18)

hp=a×Dp=Dp×[Ap/{π×(1+Dp ²)}]^(1/2)  (19)

Rp={Ap×(1+Dp ²)/(4πDp ²)}^(1/2)  (20)

that form the values for each support point.

The process for forming the oxidation film on the wafer using thepreviously described oxidizing device in the IC manufacturing method isdescribed next.

In the process for forming the oxidation film as shown in FIG. 1, theboat 21 supporting multiple arrayed wafers 1 is loaded onto the seal cap20 with the wafer 1 group arrayed along a vertical direction. The boat21 is raised upward by a boat elevator and loaded from the furnaceopening 14 of the process tube 12 into the processing chamber 13 (boatloading), and is positioned in the processing chamber 13 while stillsupported on the seal cap 20. In this state, the seal cap 20 joins via aseal ring to seal the processing chamber 13 is in an air-tight state.

In the state where the processing chamber 13 is sealed air-tight, theinterior of the processing chamber 13 is evacuated via the exhaust line33, heated to a specified temperature by the heater unit 18, and whenthe temperature of the wafers stabilizes after reaching the processingtemperature (for example 1000 to 1200° C.), then oxygen gas and nitrogengas of specified flow quantities are respectively supplied to theprocess gas supply line 38 via the oxygen gas supply line 41 and thenitrogen gas supply line 43.

The oxygen gas and nitrogen gas supplied to the process gas supply line38, is fed to the supply pipe 37 from this process gas supply line 38,and supplied via the supply pipe 37 to the gas pool 16 of the processtube 12. The process gas supplied to the gas pool 16 is uniformlydispersed across the entire interior of the processing chamber 13through the flow holes 15.

The process gas dispersed uniformly in the processing chamber 13 flowsdownward while making respective uniform contact with the multiplewafers 1 supported in the boat 21, and is exhausted from the exhaustpipe 32 by the exhaust force of the exhaust line 33 to outside theprocessing chamber 13. An oxidation film is then formed on the surfaceof the wafers 1 by an oxidation reaction due to the process gascontacting the surface of the wafers 1.

The supply of oxygen gas and nitrogen gas to the processing chamber 13is stopped after the preset processing time has elapsed. After thenpurging the sections such as the processing chamber 13 and the gas pool16 with nitrogen gas, the boat elevator lowers the seal cap 20, and theboat 21 is loaded out from the processing chamber 13 to the standbychamber 11 b (boat unloading).

After boat unloading is completed, the wafer discharging step isexecuted in order to extract the now processed wafers 1 from the boat21.

The oxidizing device then batch processes the wafers by repeating theabove described actions.

In this oxidation film forming process, damage is usually formed on thewafer rear surface due to the wafer's own weight from contact betweenthe wafer and protrusions of the support portion, and the strain causedby this damage is thought to cause slipping. The technology of prior arttherefore attempted to reduce the friction force acting between thewafer and the support portion, by smoothing the wafer supporting surfaceand eliminating protrusions.

However, slips that were not caused by damage from protrusions weresometimes confirmed to occur when the surface on the support portion wassmoothed too much. Here, excessive smoothing of the support portionsurface induces an adhesive force at the boundary between the wafer andsupport portion so that slipping occurred when the wafer and supportportion stuck to each other were separated.

The present embodiment is capable of preventing slips due to damage fromprotrusions dealt with as problems in the prior art and slips due to theadhesive force occurring due to excessive smoothing by setting thesupport portion namely, the support surface 26 of the support groove 25of the boat 21 to a surface roughness (Ra) between 10⁻⁶ m and 10⁻³ m.

The above described embodiment yields the following effects.

1) The production yield of the oxidizing device and therefore the entireIC manufacturing method can be improved since occurrence of slips can beprevented in the wafer portion where the wafer and the support portionmake contact during the oxidation process by the oxidizing device bysetting the surface roughness (Ra) of the support portion which contactsand supports the wafer between 10⁻⁶ m and 10⁻³ m.

2) The adhesive force in the contact portion of the silicon wafer andthe support portion can be set to a specific value by making the supportportion from silicon carbide so that slips can be prevented fromoccurring in the portion of the wafer which contacts the support portionduring the oxidation process by the oxidizing device by setting thedegree of cut-in to lower than a specified value, and setting thesurface roughness (Ra) of the support portion between 10⁻⁶ m and 10⁻³ m.

FIG. 8A and FIG. 8B show the oxidizing device of another embodiment ofthe present invention. FIG. 8A is a plane cross sectional view showingthe support groove section of the boat. FIG. 8 b is a partially omittedfront view.

The point where this embodiment differs from the previous embodiment isthat the support tool includes a wafer holder 29 functioning as thesupport plate which contacts the wafer, and a main body for supportingthe wafer holder 29 as the support plate; and that the wafer 1 issupported by the wafer holder 29.

The wafer holder 29 of this embodiment is comprised of a circular platemade of silicon, and has a silicon carbide film or a silicon nitridefilm whose hardness is greater than silicon on the surface of the plate.

Silicon oxide film with a hardness lower than the silicon may be formedon the surface of the circular plate made of silicon in the wafer holder29.

The wafer holder 29 may also be made from silicon carbide.

The diameter D₂₉ of the wafer holder 29 is set from approximately ⅔rdsof the diameter D₁ of the wafer 1 to less than the diameter D₁ of thewafer 1, and preferably is set from 63 to 73 percent of the diameter D₁of the wafer 1, and more preferably is set from 65 to 75 percent of thediameter D₁ of the wafer 1.

For example, when the wafer diameter D₁ is 300 mm, then the diameter D₂₉of the wafer holder 29 is set from approximately 200 mm to 300 mm, andpreferably from 190 to 220 mm, and more preferably from 195 to 210 mm.

The surface roughness (Ra) of the surface contacting the wafer 1 of thewafer holder 29 is set from between 10⁻⁶ m (1 μm) and 10⁻³ m (1000 μm),and preferably is set from 1.5 μm to 1000 μm, and more preferably is setfrom 2 μm to 1000 μm.

The method for setting the diameter of the wafer holder 29 which is thecharacteristic of the present embodiment is described next.

FIG. 9 is a graph showing analysis results relating to the displacementat the center, and the support position and wafer end in the model wherethe wafer is supported by the wafer holder (hereafter called waferholder support model), and the model where the wafer is supported atfour points (hereafter called 4-point support model).

In FIG. 9, the solid line curve indicates the wafer holder supportmodel, and the broken line curve indicates the 4-point support model.

FIG. 10A and FIG. 10B are diagrams showing the model utilized in theanalysis. FIG. 10A is for the wafer holder support model and FIG. 10B isfor the 4-point support model.

In FIG. 10A and FIG. 10B, the numeral 1 denotes the wafer, 29 denotesthe wafer holder, and 61, 62, 63, 64 denote the four support points.These four support points are respectively disposed at a mutual 90degrees phase differential on a radius r identical to the radius r ofthe wafer holder 29. The numerals 71 through 75 are measurement points.A first measurement point 71 is positioned at the center ◯ of the waferholder support model; and a second measurement point 72 is positioned onthe edge of the wafer 1 of the wafer holder support model. A thirdmeasurement point 73 is positioned at the center ◯of the 4-point supportmodel, a fourth measurement point 74 is positioned on the edge of thewafer 1 along a line extending from the center ◯ of the wafer throughthe fourth support point 64. A fifth measurement point 75 is positionedon the edge of the wafer 1 along a straight line extending from thecenter ◯ of the wafer through the center point between the adjoiningfirst support point 61 and fourth support point 64.

From FIG. 9, it can be seen that the minimum displacement can beattained by setting the support positions to a position of radius of 95mm to 110 mm from the center of the wafer, and preferably 97.5 mm to 105mm, or more preferably approximately a 100 mm position, regardless ofwhether using the wafer holder support model or 4-point support model.

However, in the 4-point support model the displacement is 0 mm at thefourth measurement point 74 positioned along a line extending from thewafer center through the support point. However, the fifth measurementpoint 75 positioned at the center point between adjoining supportpoints, sags slightly downward (−0.016 mm). More precisely, in the4-point support model there is a difference in displacement in aconcentric state due to the support point positions (angle or phasedifferential).

In other words, as shown in FIG. 8A and FIG. 8B, there is no problem dueto displacement from the weight of the wafer 1 itself, if the wafer 1whose radius is 150 mm; or in other words whose diameter of 300 mm, issupported by the wafer holder 29 whose radius is 95 mm, preferably 97.5mm or more preferably 100 mm; or in other words whose diameter of 190mm, or preferably 195 mm, or still more preferably 200 mm or more.

The diameter of the wafer holder 29 in other words may be set to 63percent or more of the wafer 1 diameter, or preferably 65 percent, orstill more preferably ⅔rds or more of the wafer 1 diameter.

However, in the present embodiment, in view of the need for a space toinsert the tweezers of the wafer transfer equipment for giving andreceiving the wafers 1 from the wafer holder 29, the diameter of thewafer holder 29 is set from approximately ⅔rds of the wafer 1 diameterto less than the wafer 1 diameter, and preferably is set to 60 percentor more and 73 percent or less of the wafer 1 diameter, and still morepreferably is set to 63 percent or more and 73 percent or less of thewafer 1 diameter.

Heat treating was performed at 1350° C. to evaluate the surfaceroughness Ra as a microscopic surface shape, understanding the waferholder support model and 4-point support model as a macroscopic supportshape.

FIG. 11A and FIG. 11B show results of the heat treating in the 4-pointsupport model at a position of radius of 100 mm. FIG. 11A is anobservation photograph of the entire surface of the wafer by a surfaceinspection device. FIG. 11B is an optical microscope photograph of thewafer rear surface.

The chain line in FIG. 11A and FIG. 11B is a circle with a radius of 100mm. The wafer is supported at the intersection with the diagonal line onthe circumference.

Results from the surface inspection device confirmed the presence ofslips (cross marks shown by arrows in the figure) at all four supportpoint locations.

As shown in the microscope photograph of the wafer rear surface in FIG.11B, the stress caused by deformation due to the wafer's own weight andheat expansion during rises and falls in temperature, concentrates onthe wafer support points and damage is formed. It is thought that damageserves as start points to cause slips.

FIG. 12A and FIG. 12B show results from heat treating in the waferholder support model that is 180 mm in diameter. FIG. 12A is anobservation photograph of the entire surface of the wafer by a surfaceinspection device. FIG. 12B is an optical microscope observationphotograph of the wafer rear surface.

The chain line in FIG. 12A and FIG. 12B is a circle with a 180 mmdiameter (90 mm radius).

The vertical line and the horizontal line in FIG. 12A and FIG. 12Brespectively indicate slips. The point where the vertical line and thehorizontal line intersect is the start point for the slips.

In FIG. 12A, a large quantity of slips can be confirmed from a locationthought to be the edge of the wafer holder.

In FIG. 12B, a row of damages can be observed along the wafer holdercontour, and these damages were confirmed to be the start point for theslips. In this case also, it is thought that the stress caused bydeformation due to the wafer's own weight and heat expansion duringrises and falls in temperature, concentrates on the wafer support pointsto form damage that serves as start points to cause slips the same as inthe 4-point model.

The diameter of the wafer holder was set from 190 mm to 220 mm, andpreferably from 195 mm to 210 mm, for example to 200 mm from the aboveevaluation results, the surface roughness (arithmetical averageroughness) Ra was found as described next, and a heat treatingevaluation was made based on surface roughness conditions centering onthat surface roughness.

The surface roughness (arithmetically averaged roughness) Ra is found byintegrating that surface cross-section function f(x) and dividing by theintegration interval. A deriving method is simply shown using the modelin FIG. 13.

In FIG. 13, setting the section with the continuous arc as the supportsurface allows expressing that surface roughness Ra with the followingformulas.

$\begin{matrix}{{Ra} = {{\frac{1}{2a}{\int_{- a}^{a}{{f(x)}{x}}}} - {2{a\left( {R - h} \right)}}}} & (21)\end{matrix}$

The equation (f(x)) for the circle (protrusion cross section) is:

f(x)=(R ² −x ²)^(1/2)  (22)

and the surface area S (protrusion cross section area) enclosed by thethick line is as follows:

$\begin{matrix}{\begin{matrix}{S = {{\int_{- a}^{a}{{f(x)}{x}}} - {2{a\left( {R - h} \right)}}}} \\{= {{\int_{- a}^{a}{\left( {R^{2} - x^{2}} \right)^{1/2}{x}}} - {2{a\left( {R - h} \right)}}}} \\{= {{R^{2}\theta \; a} - {a\left( {R - h} \right)}}}\end{matrix}{{Here},{{Ra} = {{S/2}a}},}} & (23) \\{{Ra} = {{\left\{ {{R^{2}\theta \; a} - {a\left( {R - h} \right)}} \right\}/2}a}} & (24)\end{matrix}$

so that the surface roughness Ra is expressed as a function of theradius of curvature (R).

FIG. 14 is a graph showing the relation between the maximum surfaceheight Ry and the surface roughness Ra of the wafer holder with adiameter of 200 mm for wafers (x marks in FIG. 14) where slips caused bydamage were confirmed, and wafers that were slip-free (⋆ marks in FIG.14).

Slip-free wafers with a diameter of 300 mm were verified in the heattreating process at 1350° C. However, slips were confirmed in theleft-side region in FIG. 14 (“Slip-occurs” region). Wafers where slipsoccurred were also confirmed in the center region in FIG. 14 (“Mixed”region). A stable, slip-free state was confirmed on multiple wafers onthe right edge area (“Slip-free” region).

The boundary value between the surface roughness Ra in the slip-occursregion and the surface roughness Ra in the mixed region wasapproximately 1 μm, and the boundary value between the surface roughnessRa in the mixed region and the surface roughness Ra in the slip-freeregion was approximately 1.5 μm.

Also, setting the wafer holder surface roughness Ra to a value of 2.0 μmwas confirmed to definitely attain a slip-free state.

The adhesive force can here be substituted for the friction force aspreviously described in FIG. 4 through FIG. 7.

Then, when the radius of curvature of the protrusion which correlateswith the surface roughness Ra becomes small, the friction coefficientbecomes larger so that the adhesive force increases.

Conversely, when the radius of curvature of the protrusion becomeslarge, the friction coefficient becomes small so that the adhesive forceis reduced.

If the radius of curvature of the protrusion is less than 1 μm whencalculating the stress from this friction coefficient, then the totalstress exceeds the wafer yield stress so that slips occur. However, itis found that no slips occur if the radius of curvature of theprotrusion is 1 μm or more.

However, if the radius of curvature of the protrusion is exactly 1 μmthen there is little margin so that slips might possibly occur. Settingthe radius of curvature of the protrusion to 1.5 μm makes a much largermargin so that there is a very high probability that slips can beprevented. Setting the radius of curvature of the protrusion to 2 μmfurther increases the probability that no slips will occur.

On the other hand, achieving a slip-free state is impossible when theupper limit of 1,000 μm of the wafer holder surface roughness Ra hasbeen exceeded, because maintaining that level of machining precision inactual surface processing of the wafer holder is not practical.

Moreover, results identical to those shown in FIG. 14 were confirmedeven when the wafer holder diameter was varied between 190 mm to 220 mm.

However, the results obtained in FIG. 14 were not obtained when thewafer holder diameter was set below 180 mm, and when the wafer holderdiameter was set to 230 mm or more.

The reasons for these results are as follows.

Whether or not slips will occur on a wafer is not determined just by thesurface roughness Ra of the wafer holder portion which contacts thewafer, and is also dependent on the contact surface area of the waferholder which contacts the wafer (wafer holder diameter) and the wafersupport locations on the wafer holder.

For example, during heat treating at a specific temperature (forexample, 1350° C.), even when supporting a 300 mm diameter wafer on awafer holder with the specified surface roughness Ra (for example, 2.0μm), when the wafer holder diameter or in other words, the contactsurface area between the wafer and the wafer holder or the wafer supportlocations by the wafer holder changes, then in some cases slips willoccur, and in some cases slips will not occur on the wafer.

Accordingly, when supporting a wafer on a wafer holder whose diameter isbetween 190 mm to 220 mm so that the wafer displacement (deflection)will be a minimum, then both slips caused by excessive smoothing thewafer holder and slips caused by damage from protrusions on the waferholder surface can be prevented by setting the wafer holder surfaceroughness Ra from 1 μm to 1,000 μm, and preferably 1.5 μm to 1,000 μm,and still more preferably from 2 μm to 1000 μm. However, when the waferholder diameter is 180 mm or less, and when the wafer holder diameter is230 mm or more, or in other words, the wafer displacement (deflection)is comparatively large, then at least one of either slips caused bydamage from protrusions on the wafer holder surface or slips caused byexcessive smoothing the wafer holder will occur even if the wafer holdersurface roughness Ra is set from 1 μm to 1,000 μm, and preferably 1.5 μmto 1,000 μm, and still more preferably from 2 μm to 1000 μm.

FIG. 15A and FIG. 15B are views showing the processing results when awafer holder was used whose surface roughness Ra was in the“Slip-occurs” region. FIG. 15A is an observation photograph made by asurface inspection device. FIG. 15B is a microscope observationphotograph of slips from damage as a start point.

Slips concentrated in the vicinity of the wafer center were confirmed.

The reasons for these results are as follows.

A large adhesive force Fa occurs between the wafer and support portion(wafer holder) due to the small surface roughness Ra. Slips occurred asthe heat treat progressed in a state where the wafer and the supportportion adhered in the vicinity of the wafer center. Proof of the slipsappears in FIG. 15B as traces at the rear surface of the wafer showing asection of the support portion or in other words the surface of thewafer holder was peeled away, and slips were further observed due tothis impact.

FIG. 16A and FIG. 16 B are views showing the processing results when awafer holder was used whose surface roughness Ra was in the “Slip-free”region. FIG. 16A is an observation photograph made by X-Ray topograph.FIG. 16B is a microscope observation photograph showing small damages onthe wafer holder edge.

No slips at all were observed on the wafer. However, small damage isformed on the circumference on the wafer holder edge as shown in themicroscope photographs. No slips could be confirmed from the smalldamage on the surface inspection device, X-ray topograph and bymicroscope observation. The small damages were present on the entiresurface contacting the wafer holder though they were too small to beverified by X-ray topograph. They could however be observed bymicroscope, which is proof that the tiny protrusions present for theentire region at the boundary between the wafer and support portionnamely, the wafer holder dispersed friction force Ff with a goodbalance.

The present invention is not limited to the examples in the aboveembodiments and needless to say, changes of different types notdeparting from the spirit or the scope of the present invention arepermitted.

The wafer holder for example, is not limited to a structure where thesurface of the silicon plate is covered with a material harder thansilicon, such as silicon carbide film or silicon nitride film, and maybe a structure where the silicon plate surface is covered with amaterial whose hardness is smaller than silicon, such as silicon oxidefilm, and may also be a structure of silicon carbide plate or a siliconnitride plate.

A least one through-hole may also be formed in the wafer holder. Formingthis type of structure allows air between the wafer and wafer holder topass through the through-holes outside when transferring the wafer tothe wafer holder, and can prevent wafer slip on the wafer holder. Awafer holder with this type of structure also can prevent both slipscaused by excessive smoothing of the wafer holder, and slips caused bydamage from protrusions on the wafer holder surface.

A process for forming an oxidation film on the wafer in an ICmanufacturing method was described in the above embodiment. However, theheat treating apparatus of the present invention may also be applied toother heat treating processes in IC manufacturing methods.

The present invention may be preferably applied in particular to heattreating processes performed at comparatively high temperatures such asthermal oxidation processes including dry oxidation, wet oxidation,hydrogen pyrogenic oxidation, and hydrochloric acid (HCl) oxidation; andthermal diffusion processes for diffusing dopants such as boron (B),phosphorus (p), arsenic (As), antimony (Sb) into semiconductor thinfilm; and annealing processes, etc.

Applying the heat treating apparatus of the present invention to heattreating processes of these types for IC manufacturing methods canprevent wafer slips from occurring.

Moreover, the heat treating apparatus of the present invention exhibitsexcellent effects when applied to method for manufacturing substrates.

The application of the heat treating apparatus of the present inventionfor example to heat treating processes in SIMOX (separation by implantedoxygen) wafers which are one type of SOI (silicon on insulator) wafersis described next.

First of all, an ion implantation device, etc. implants oxygen ions intothe single crystal silicon wafer. After ion implantation, the oxygen ionimplanted wafer is then subjected to annealing at high temperatures ofapproximately 1300° C. to 1400° C. (for example, 1350° C. or more) infor example an argon (Ar) atmosphere or oxygen (O₂) atmosphere by theheat treating apparatus of the present invention. These processes inthis way manufacture a SIMOX wafer with a silicon oxide (SiO₂) layerformed (with a silicon oxide layer embedded) in the interior of thewafer.

The heat treating apparatus of the present invention can also be appliedto heat treating processes in hydrogen annealed wafers manufacturingmethods. In this case also, the wafer is annealed at high temperaturesof 1200° C. or higher in a hydrogen atmosphere using the heat treatingapparatus of the present invention. Crystal flaws in the surface layersof the wafer for manufacturing the IC can in this way be reduced and thecrystalline integrity can be enhanced.

The heat treating apparatus of the present invention can also be appliedto heat treating processes for epitaxial wafer manufacturing methods.

Utilizing the heat treating apparatus of the present invention canprevent the occurrence of wafer slips even in cases where annealing athigh temperatures in the above described process for manufacturingsubstrates is performed.

The present invention is not limited to dry oxidizing devices and mayalso be applied to other general types of the heat treating apparatusincluding oxidizing devices, diffusion devices, annealing devices aswell as other treating devices, etc.

In the above embodiment, the case where silicon wafers were processedwas described, however the substrate for processing may also includegermanium wafers and compound semiconductor wafers, etc. Moreover, thepresent invention may also be applied to photo masking and printedcircuit boards, liquid crystal panels, compact disks and magnetic disks,etc.

1. A heat treating apparatus comprising a processing chamber for heattreating a substrate, and a support tool for supporting the substrate inthe processing chamber; and the support tool having a support platewhich contacts the substrate, and a main body for supporting the supportplate, wherein the diameter of the support plate is 63 to 73 percent ofthe diameter of the substrate and the surface roughness Ra of at least aportion of the support plate which contacts the substrate is set from 1μm to 1,000 μm.
 2. The heat treating apparatus according to claim 1,wherein the surface roughness Ra of at least the portion of the supportplate which contacts the substrate is set from 1.5 μm to 1,000 μm. 3.The heat treating apparatus according to claim 1, wherein the surfaceroughness Ra of at least the portion of the support plate which contactsthe substrate is set from 2 μm to 1,000 μm.
 4. The heat treatingapparatus according to claim 1, wherein the diameter of the substrate is300 mm, and the diameter of the support plate is 190 mm to 220 mm. 5.The heat treating apparatus according to claim 1, wherein the hardnessof at least the portion of the support plate which contacts thesubstrate is the same as or greater than the hardness of the substrate.6. The heat treating apparatus according to claim 1, wherein the mainbody is made from silicon carbide, and the support plate is made fromsilicon or silicon carbide.
 7. The heat treating apparatus according toclaim 6, wherein a layer of silicon oxide, silicon carbide, or siliconnitride is formed on the surface of the support plate.
 8. The heattreating apparatus according to claim 1, wherein the heat treatment isperformed at a temperature of 1300° C. or higher.
 9. The heat treatingapparatus according to claim 1, wherein at least one through hole isformed in the support plate.
 10. A method for manufacturing a substratecomprising the steps of: supporting a substrate on a support plate inwhich the diameter is 63 to 73 percent of the substrate diameter, andthe surface roughness Ra of at least the portion which contacts thesubstrate is 1 μm to 1,000 μm; loading the substrate supported on thesupport plate into a processing chamber; heat treating the substratesupported on the support plate in the processing chamber; and unloadingthe substrate from the processing chamber after the heat treating.